Ultraviolet lasers are widely used in industry. Important examples are current use of KrF and ArF excimer lasers (and the currently scheduled use of F2 excimer lasers) for lithographic fabrication of integrated circuits. These lasers typically operate 24 hours a day, 7 days per week 365 days per year with only short down times for maintenance.
Ultraviolet light generated in these lasers can damage sensitive optical components in the presence of oxygen or a wide variety of other chemicals or chemical compounds. Also, oxygen is significantly absorptive of the ArF laser beam and very absorptive of the F2 laser beam. For these reasons, a common practice is to purge sensitive optical components of these lasers with nitrogen or helium. Another known practice for reducing optical damage is to minimize the use of components or materials which out-gas chemical vapors during laser operation.
A well used technique used in the construction of these lasers is to group components into modules which can be quickly and easily replaced as a part of a maintenance program.
The path of the laser beam through a laser system is referred to as a xe2x80x9cbeam trainxe2x80x9d. Attempts have been made to seal the beam trains from the outside environment. These attempts especially attempts to seal the sections of the beam train in between modules, have often made module replacement much more difficult. Also, seals between modules may permit unwanted vibration produced in one module to be transferred to another module where the vibration adversely affects performance. This is an especially serious concern for the modules containing the optical components which form the resonant cavity of the laser and the component (sometimes called a xe2x80x9cwavemeterxe2x80x9d) that measures beam parameters such as wavelength and bandwidth.
FIG. 1 is a drawing of a prior art KrF laser system with the front doors of the laser cabinet removed. The drawing shows chamber 156, line narrowing module 120 output coupler module 130 and wavemeter 140. The direction of the output laser beam is shown at 142. Chamber 156 weighs about 200 pounds but is fitted with wheels and can be replaced quickly and easily by disconnecting two gas lines and rolling the old chamber out and rolling a new chamber in on rails as shown in FIGS. 8, 8A, 9 and 9B. In this prior art KrF laser, the portions of the beam train between the chamber and the output coupler end and between the chamber and the LNP are not sealed so problems associated with transmittal of vibration through seals and seal interference with chamber removal does not exist.
What is needed is an effective method for protecting the portion of the beam train between a laser chamber and optical equipment forming the resonant cavity of the laser while permitting easy replacement of the laser chamber.
The present invention provides beam train isolation between a gas discharge laser chamber of a modular laser system and front and rear optics defining the laser resonant cavity while permitting quick and easy removal of the laser chamber without disturbing the optics of the resonant cavity. In preferred embodiments, metal bellows units are bolted at only one side so that the chamber can be removed and replaced without unbolting the bellows unit.